Known in the art is an apparatus for automatic metering of molten metal from a bale-out furnace, comprising a metal conduit, a gas conduit and an alloy feed regulator made in the form of a gas pipe with one end thereof secured in the bale-out furnace, the other end coupled with a maximum pressure limiter, for instance, a tubular hydroseal, and the middle part associated with a gas source (SU, A, 582044).
The aforementioned prior art apparatus operates as follows.
In the initial position, the gas pressure in the bale-out furnace is equal to atmospheric, and the molten metal in the metal conduit is at the level of the bath free surface. As the gas pressure in the gas pipe increases, the gas bubbles through the molten metal, raising pressure in the bale-out furnace; as a result, the molten metal flows up the metal conduit to the preassigned level, which is subsequently maintained automatically constant, independently of the level of the molten metal in the bale-out furnace.
This apparatus assures automatic maintenance of the level of molten metal in the outlet portion of the metal conduit, irrespective of the level of molten metal in the bale-out furnace, which allows continuous metal casting.
This prior art apparatus, however, requires a pressure-tight bale-out furnace, a pressure-tight metal conduit outlet, and a pressure-tight gas pipe inlet, which makes the apparatus a batch-action arrangement, as an evacuated bale-out furnace must be depressurized, changed and re-pressurized.
Another prior art apparatus, intended for pumping out molten metal, comprises a centrifugal conduction MHD-pump placed in a reservoir with molten metal (SU, A, 67978). The MHD-pump includes a ceramic body with double walls, with a solenoid being located therebetween. A transverse partition divides the cylindrical space of the body into an upper and a lower spaces. The central part of the partition has a hole to communicate the body upper and lower spaces. The body upper space encloses a graphite electrode with a tip, and the working chamber is formed by the graphite electrode tip and the transverse partition. Molten metal from the reservoir is fed to the working chamber through the lower space in the body and the hole in the partition. Molten metal is drained through a suitable branch pipe located in the body upper space.
The apparatus also contains two d.c. sources, one of which promotes electric current flow through molten metal in the working chamber and the other serves to pass electric current through the solenoid.
Let us consider operation of the apparatus.
Metal in the reservoir is set as at a level whereat, with the power sources turned off, the working chamber is filled with molten metal. Voltage from a d.c. power source to pass electric current through the working chamber is supplied to the graphite electrode of the MHD-pump and an additional electrode located in the reservoir. The solenoid is also supplied with voltage from its own d.c. source. As a result, a magnetic field is induced in the working chamber, the field induction vector directed along the longitudinal axis of the working chamber. The direct current flowing through the molten in the working chamber interacts with the magnetic field produced by the solenoid, and sets the metal into rotation. The resultant pressure differential between the central inlet hole and the molten metal outlet branch pipe forces the metal into the latter.
The availability of two d.c. power sources makes it possible to control both the working current flowing through the molten metal in the working chamber and the current flowing through the solenoid.
It has been known that the pressure developed by the centrifugal conduction MHD-pump and also the capacity of the latter vary with the variation of both the strength of the electric current flowing through molten metal in the working chamber and the strength of the electric current flowing through the solenoid.
Therefore, the foregoing prior art apparatus for pumping out molten metal may be used for meter-feeding of molten metal into a mould, the control of the metering process boiling down to the control of the electric currents flowing through the molten metal in the working chamber and through the solenoid.
However, said prior art apparatus for pumping out molten metal is not pressure-tight and, consequently, can develop only a low pressure, its capacity drastically changes even with insignificant variation in the level of molten metal in the reservoir and, besides, it cannot be applied for heating of molten metal in a closed space while feeding metal into a mould.